A vaccine against Leishmania major in BALB/c mice using a soluble fraction of the parasite was developed. This soluble extract was further fractionated by an FPLC Mono Q column into subfractions with differing capacities to stimulate T cells and to be recognized by antibodies. Only proteins within one subfraction (fraction 9) were capable of inducing protection, although other fractions were recognized by T lymphocytes from immunized mice. While the qualitative differences between T cell antigens which do and do not induced protection are unknown, it is possible that distinct macrophage subsets may be elicited by different T cell populations. For example, we found that macrophages from non-immunized infected BALB/c mice are relatively unresponsive to activation signals, while macrophages from immunized mice are capable of killing the intracellular parasite. Current studies are focused on identification of the protective immunogen(s) within fraction 9. Since immunity in this model has been shown to be mediated by T cells, identification of the fraction 9 molecules recognized by T cells may serve this purpose. Consequently, T cell lines and clones reactive against antigens within fraction 9 were produced, and preliminary results indicate that the T cell lines can passively protect naive mice. The antigen specificity of these T cells was determined by separation of leishmanial antigens by SDS-PAGE, immunoblotting to nitrocellulose, and stimulation of T cells with small sections of the blot corresponding to defined molecular weights. Antigens in the relative molecular weight regions of 8 K to 14 K, 20 K to 30 K and 40 K to 45 K were found to stimulate the T cell line. When T cell clones were tested, one clone was found that responded specifically to the 8 K and 10 K proteins. These molecules are currently being eluted from an SDS polyacrylamide gel, and are being tested for their immunoprophylactic capacity. Finally, a polyclonal rabbit antisera raised against fraction 9 is being used to screen a Leishmania lambda gtll library for recombinants expressing proteins found within this protective fraction.